研究了承载镍催化剂的三维(3D)炭纤维预型体,在含氢或无氢条件下,乙烷和合成天然气在其上面化学气相沉积形成的炭沉积率和碳纳米构结物.观察了炭沉积所获石墨纳米纤维、碳纳米管和石墨碳壳,得知沉积碳的纳米结构取决于沉积温度和碳源气组成.在650℃～800℃温间,总沉积时程直至12h,研究了烃类碳源气在氢气平衡下,从体积分数100%到20%变化情况.经Ni(NO3)2-6H2O甲醇溶液浸渍的3D炭纤维预型体在炭沉积前因溶液分解可还原出Ni.采用质量变化测定法、热谱-质谱分析仪、SEM、TEM和XRD对样品进行表征.结果表明:纤维状炭与囊包炭的比率随氢气含量的增加而增加,随反应温度的增高而减少.出乎意料的是,氢气的添加并不延长催化剂的寿命.该工艺过程对炭/炭复合材料的制备展示出良好的潜力.
The rate of carbon deposition and the carbon nanostructures formed during the chemical vapor deposition of ethane and synthetic natural gas, with and without added hydrogen, over a nickel catalyst, supported on three-dimensio-nal (3D) carbon fiber preforms, was investigated. Graphitic nanofibers, carbon nanotubes, and graphitic carbon shells were observed following carbon deposition; the nanostructured carbon deposited was dependant on deposition temperature and gas feedstock composition. Gas feedstocks ranging from volume fraction 100 to 20% hydrocarbon with a balance of hydrogen were investigated at temperatures ranging from 650 to 800℃, up to 12h total deposition time. The 3D carbon fiber supports were impregnated with a methanolic solution of nickel nitrate hexahydrate that was decomposed and re-duced to nickel before carbon deposition. The samples were characterized using weight change measurements, thermo-gravimetric analysis coupled to a mass spectrometer, scanning and transmission electron microscopy, and X-ray diffrac-tion. Analysis of the samples revealed an increase in the ratio of filamentous to encapsulation with increasing hydrogen content with the reverse being observed with increasing temperature. Unexpectedly, it was found that hydrogen addition did not extend the lifetime of the catalyst. This process shows good potential for the manufacture of carbon-carbon com-posites.
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